Conventionally, as non-contact charging techniques of a strongly-coupled system using the alternate current, for example, systems using electromagnetic induction, electric-field coupling, magnetic-field resonance, electric-field resonance and the like have been known. Then, in a non-contact charging apparatus used in the non-contact charging techniques of a strongly-coupled system using the alternate-current mentioned above, the matching of the impedance of the electric power-supply system that supplies the alternate-current power and the impedance determined by the power transmitting unit and the power receiving apparatus (power transmitting/receiving system) is essential. That is, without the impedance matching, a reflected power is generated between the power supply unit and the power transmitting unit and affects the power supply system. In addition, due to the influence of the reflected power, it leads to Electromagnetic Interference (EMI) to the peripheral devices. Furthermore, it also reads to a decrease in the efficiency in the non-contact charging apparatus. Particularly, the influence is significant when a large electric power is transmitted. For example, charging to a battery mounted on an electric vehicle and a hybrid vehicle may be considered.
As a related art, a non-contact power transmitting apparatus including an alternate-current power source, a primary coil connected to the alternate-current power source, a primary-side resonance coil, a secondary-side resonance coil, a secondary coil to which a load is connected, and an impedance variable circuit provided between the secondary coil and the load has been known. The primary coil, the primary-side resonance coil, the secondary-side resonance coil, the secondary coil, the load and the impedance variable circuit constitute a resonance system. The alternate-current power source outputs an alternate-current voltage in a frequency equal to the resonance frequency of the resonance system. The impedance of the impedance variable circuit is adjusted so as to suppress the change of the input impedance of the resonance system. As a result, even when at least one of the distance or the load between the two resonance coils change, it is possible to supply the electric power from the alternate-current power source to the load with a good efficiency, without changing the frequency of the alternate-current output voltage of the alternate-current power source.
Patent document 1: Japanese Laid-open Patent Publication 2010-141977